Sheet molding compounds (SMC) are a paste reinforced with glass, carbon, or natural fibers. The paste is generally a polyester resin filled with calcium carbonate and other additives. While fibers are initially randomly oriented in the plane of the sheets, forming processes such as compression molding or extrusion causes orientation of the fibers and a surface skin with few fibers exposed. Due to both their specific mechanical and electrical properties and their cost-efficient processing, these materials are widely used by the automotive industry and by the electrical industry to produce rigid and lightweight parts. The resulting parts are characterized by surfaces that are not electrical conductive and prone to surface energy inhomogeneities that make it difficult to obtain the high gloss surface needed for many vehicle applications.
Graphene is processed by chemical exfoliation to yield graphene oxide. Graphene oxide has a variety of reactive moieties including hydroxyl, epoxy and carboxyl groups. The sheet-like structure of graphene oxide and the conjugated ring structure make this attractive as an additive to modify the surface properties of SMCs. Unfortunately, for all the potential properties of graphene oxide, the conductivity and surface energies that would result from a sub-monolayer surface layer of graphene oxide are inadequate to meet production needs for mass production of parts. Additionally, compatibility of graphene oxide with high-density inorganic fillers, such as calcium carbonate, carbon fibers, and thermoplastic low profile additives present to improve the surface remain a challenge while attempting to improve processing while maintaining surface quality characteristics.
While attempts have been made to modify resin backbones to include graphene oxide, such efforts have met with limited success owing to complications in maintaining properties of existing, qualified resins. Additionally, owing to viscosity and molecular weight of thermoset resin prepolymers, appreciable amounts of graphene oxide are required to fill the matrix volume with graphene oxide, even though such properties are often preferentially desired at the surface of a molded article.
Thus, there exists a need for a monomer containing a modified graphene oxide for improved surface conductivity in SMC or BMC article molding.